Various types of conveyor support bars for use in paper making machinery are known. Typically, such support bars are positioned beneath and extend transversely across the path of movement of a conveyor of a paper making machine to supportably engage the undersurface of the conveyor. In the Fourdrinier type paper making machine, the bars are particularly shaped and spaced beneath the screen carrying the paper pulp slurry to provide for vacuum removal of water from the slurry on the upper surface of the screen during the paper making operation. Such water removal bars, also known as foils or blades, can be employed with positive suction boxes below the screens, or their upper surfaces may be angled so as to create a suction effect beneath the screen surface to draw the water from the pulp slurry carried thereon as the screen moves longitudinally thereover.
Such water removal foils and support bars are of a continuous length to span the width of the longitudinally moving screen and may be of a length of as much as forty feet for this purpose. A high degree of accuracy and alignment of the bar with the moving screen is required to ensure proper seal for water removal from the slurry, and to reduce the wear on the screens during the paper making process.
To increase wear resistance of the bars, and reduce wear on the screens engaged thereby, it has been a practice to construct the bars with a hard, smooth, wear-resistant nose portion formed of a metal alloy or a ceramic material, such as alumina, which engages the surface of the screen. The wear-resistant nose, or blade, portion is adhesively bonded in a resinous material, such as an epoxy resin, which is in turn adhesively secured to a base member, such as polyethylene. The polyethylene base member is provided with an elongate channel which is slidably received on a fixed transverse support member of the frame of the paper making machine.
Such bars are strengthened by elongate metal channel members which are embedded within the epoxy resin and extend along the length of the bar to provide dimensional support thereto during installation and use. The wear-resistant nose portion of the bar which sealingly engages the undersurface of the moving screen is generally composed of a plurality of short ceramic plates positioned in endwise abutment in the epoxy resin along the length of the bar, and the ends of the plates are interconnected by metal pins disposed in mating grooves of the plates to position the plates in surface alignment for continuous engagement with the undersurface of the conveyor screen. Support bars of the type herein described are disclosed in prior U.S. Pat. Nos. 3,393,124; 4,106,981; Canadian Pat. No. 1,029,996; and Italian Pat. Nos. 789,972 and 917,248.
Although metal-reinforced support foils and bars with ceramic nose portions find wide use in the paper making industry, many problems are encountered in their use because of stresses and forces which act on the bar as a result of differential thermal expansion and contraction of the different composite materials employed therein. The differential thermal expansion and contraction of the metal reinforcing components which are embedded in the resinous components of the bar work against the expansion and contraction of the resinous components to cause cracking and delaminating of the bars after a time of use. Such differential forces acting on the bar also often cause displacement and improper alignment of the ceramic plates of the nose portion of the bar which engage the undersurface of the screen, resulting in non-uniform water removal from the slurry and greater wear on the screens, necessitating periodic replacement of the screens and bars during the paper making process.